white as a sheet

Example: “She came out of the haunted house white as a sheet.”

Origin: The pallor is real and involuntary. Fear and shock trigger the body to constrict the blood vessels near the skin and redirect blood toward the core and the large muscles, so a frightened person genuinely does drain of color within seconds — a physiological response, not a literary exaggeration, and one visible enough that observers have always had reason to name it. The sheet supplies the standard of whiteness: bleached linen bedding was among the whitest objects in an ordinary household, kept deliberately so, and therefore the obvious thing to measure sudden pallor against. The comparison is attested in English from the 1700s, and it displaced a crowd of older variants built the same way — pale as ashes, white as a cloth, white as a ghost.